3-D projection full color multimedia display

ABSTRACT

Methods and systems are described herein which produce polarization-independent full color images suitable for rear-projection television sets and other multimedia displays. The system uses illumination with R, G, B light from two different light sources for each color. A viewer wears glasses with narrowband optical filters, preferably holographic filters. The R, G, B light from the light sources is slightly offset at each of the 3 emission wavelengths, with one set of R, G, B light being filtered by the holographic filter in front of the left eye of the, and the other set of R, G, B light being filtered by the holographic filter in front of the viewer&#39;s right eye.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/794,669, filed Apr. 25, 2006, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Various techniques have been used in the past to produce stereoscopic(three-dimensional) images for motion pictures or television. Ingeneral, these techniques involve two camera systems in which twodifferent pictures are taken from slightly different camera angles andlocations. The object is to simulate the manner in which depth isperceived by a pair of human eyes, which are themselves slightly offsetfrom each other and thus view images at slightly different angles. Thetwo camera images are superimposed and presented to the viewersimultaneously on a television or movie screen. The images are thenseparated in some fashion for the viewer so that one eye sees only oneimage, and the other eye sees only the other image.

One technique which has been used to implement this approach is calledthe anaglyphic 3-D process, and has been employed in earlier 3-D motionpictures. This technique uses color filters to separate the two images.The images are color coded, for example with red and blue/green,respectively, and the viewer is provided with glasses having differentcolored filters in front of each eye. Each filter rejects the image thatis not intended for that eye, and transmits the image which is intendedto be seen by that eye. A red color filter will pass only the red image,while a blue/green color filter will pass only the blue/green image. Ifthe left eye image is presented as a red image and the right as ablue/green image, and a blue/green filter is placed in front of theright eye and a red filter in front of the left eye, the proper imageswill be directed to the proper eye and a 3-D image will be perceived bythe viewer.

The anaglyphic 3-D process is advantageously inexpensive to implementand can be used with any type of screen or display medium, as long asthe colors can be effectively separated. Typically, two projectors arerequired, one for the red image, and another for the blue/green image.However, color filters which fully reject the undesired image aredifficult to make, with the result that the 3-D effect is impaired. Asignificant disadvantage therefore remains in that the image isessentially interpreted in the brain as a black and white image or isonly capable of producing drab colors at best, which is unappealing tothe typical consumer. The images are generally of poor quality withperceptible shadowing, and may cause discomfort to the viewer, such aseye fatigue and/or nausea.

Another 3-D process used in motion pictures uses polarized light, inwhich the left and right eye images are separated by the use ofpolarizing light filters or other polarizing elements known in the art.The left eye image is projected onto the screen through a polarizingfilter rotated by, for example, 45° to the left of vertical, while theright eye image is projected onto the screen through a polarizing filterrotated 45° to the right of vertical. In this way the polarization ofthe two images are at right angles, and similarly polarized filtersplaced in front of each of the viewer's eyes will cause the proper imageto be transmitted to each eye. This method produces high-quality images,but disadvantageously also requires two projectors, goggles withhigh-quality polarizing filters for viewing, and a specialpolarization-maintaining projection screen. Moreover, the 3-D image willwash out if the viewer tilts his/her head too much or moves around toofar.

Another technique which has been used to produce 3-D images of motionpictures involves the sequential presentation of left and right eyeimages to the viewer, wherein the alternate left and right eye imagesare projected so that the polarization of the two images is at rightangles, at described above. To be perceived by the viewer as acontinuous motion, each of the left and right eye images would need tobe projected at twice the conventional frame rate of 24 frames/second. Asingle projector, for example, a digital light processing system (DLP)from Texas Instruments, capable of projecting 48 frames/second could beused to project the image with alternating polarization.

Another approach uses a field sequential technique. This is accomplishedby means of sequentially recording the left and the right scenes(fields) and then sequentially displaying them in the same order withproper synchronization. Each viewer would be provided with synchronizedelectro-optical glasses to switch on the filter in front of each eyewhen its image is being presented. This process is complicated andexpensive, and requires special equipment for broadcasting the triggersignals to the electro-optical glasses worn by each user.

It therefore becomes evident, that a full color 3-D television and/ormultimedia display that can be viewed with relatively inexpensiveglasses/goggles has mostly included generation of polarized imagesintended for the left and right eye by a projection method. Conventionalmethods to date have required a polarization-maintaining projectionscreen. However, the conventional methods cannot be used with, forexample, rear-projection television (RPTV) sets, because thepolarization becomes completely random when the image passes through thescreen of the RPTV and as a result, the 3-D effect gets lost.

Accordingly, a new approach is required for displaying 3-D colortelevision images with RPTV sets that do not rely on polarizationeffects to separate the images for the left and right eye.

SUMMARY OF THE INVENTION

In aspect, the invention relates a method of displaying athree-dimensional image. The method includes displaying a first seriesof images intended to be viewed by the right eye of a viewer. Theseright eye images are displayed by illuminating a light modulator with afirst color. A first series of images intended to be viewed by the lefteye of a viewer are also displayed. Each image in the series of left eyeimages corresponds to an images in the series of right eye images. Thefirst series of left eye images are displayed by illuminating the lightmodulator with a second color. The second color is substantially thesame as, but not identical to the first color. A viewer is provided witha filter for filtering out the first color and a filter for filteringout the second color.

In one implementation, the method includes displaying a second series ofleft eye images and a second series of right eye images. Each image inthe second series of left eye images and right eye images correspond torespective images in the first series of left eye images and right eyeimages. The second series of left eye images and second series of righteye images are displayed by illuminating the light modulator with athird and a fourth color, respectively. The third and fourth colors aresubstantially the same, but they are not identical. They are alsosubstantially different from the first and second colors. In oneembodiment, the first and second colors correspond to a first primarycolor and the third and fourth colors correspond to a second primarycolor. The left eye filter filters out the third color and the right eyefilter filters out the fourth color.

In one implementation, the same light modulator is used to modulate allthe images. In another implementation, one light modulator is used tomodulate the first and second colors and a different light modulator isused to modulate the third and fourth colors. In still anotherimplementation, a separate modulator is employed to modulate each color.In various embodiments, the light modulators are illuminated by a laser,a laser array, a light emitting diode, or a lamp having an associatedcolor wheel.

The first and second colors, in one embodiment, are both perceived by auser either red, green, blue, magenta, cyan, or yellow. The third andfourth colors are both perceived by a user as a different primary color.The colors have a bandwidth with a center wavelength. Preferably, thecenter wavelengths of the first and second colors differ by about 10 nm.In one implementation, the bandwidths of the first and second color donot overlap.

According to another aspect, the invention relates to a system fordisplaying a three-dimensional image. The system includes a first lightsource providing a first illumination color and a second light sourceproviding a second illumination color. The second illumination color issubstantially the same as, but not identical to the first illuminationcolor. The system also includes a light modulator, for example, an arrayof micromirrors or a liquid crystal on silicon array, for modulatinglight emitted by the first and second light sources to generate twoseries of images. The system also includes a processor for alternatinglyaddressing the light modulator with images from the first and secondseries of images. Images in a second series correspond to respect imagesin the first series. In addition, the system includes projection opticsfor displaying the two series of images on a display screen.

In various embodiments, the first and second light sources includelasers, arrays of lasers, light emitting diodes, and a lamp withcorresponding filters included on a color wheel. In embodiments in whicheach light source includes an array of lasers, the light source alsoincludes optics for combining the light output by the array of lasers toform the first illumination color. In one embodiment, the light in thefirst illumination color is centered at a wavelength that is 10 nm apartfrom a center wavelength of the light included in the secondillumination color. In one embodiment, the system include third andfourth light sources emitting substantially similar, but not identical,colors of light. The colors emitted by the third and fourth lightsources is substantially different than the colors emitted by the firstand second light sources.

The system includes viewing glasses that include a left eye filter and aright eye filter. The left eye filter filters out the first series ofimages and the right eye filter filters out the second series of images.The left eye and right eye filters each include a plurality of notchfilters, preferably thin-film holographic notch filters, tuned to blockthe wavelengths of light emitted by the first and third and second andfourth light sources, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description which follows, reference will be made to theattached drawings, in which:

FIG. 1 is a system diagram for presenting 3-D images using arear-projection television, according to an illustrative embodiment ofthe invention.

FIG. 2 is a block diagram of the rear-projection television of FIG. 1,according to an illustrative embodiment of the invention.

FIG. 3 is a block diagram of an optical pathway in the rear-projectiontelevision of FIG. 1, according to an illustrative embodiment of theinvention.

FIG. 4 is a block diagram of an optical pathway in the rear-projectiontelevision of FIG. 1, according to a second illustrative embodiment ofthe invention.

FIG. 5 is a block diagram of a system for providing a laser illuminationsource yielding reduced speckling, according to an illustrativeembodiment of the invention.

FIG. 6 is a graph illustrating wavelengths of light sources for use inan illustrative embodiment of the invention.

DETAILED DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS

To provide an overall understanding of the invention, certainillustrative embodiments will now be described, including variousapparatus and methods for forming three-dimensional images. However, itwill be understood by one of ordinary skill in the art that theapparatus and methods described herein may be adapted and modified as isappropriate for the application being addressed and that the systems andmethods described herein may be employed in other suitable applications,and that such other additions and modifications will not depart from thescope hereof.

Systems and methods are described that can be used to produce afull-color projection image on a non-polarization maintaining screen,such as a RPTV. The systems and methods are based on the concept thatalmost any point in color space is accessible by a combination of threedistinct colors, red (R), green (G), and blue (B). An additive colorsystem involves light emitted directly from a source or illuminant ofsome sort. The additive reproduction process usually uses red, green andblue light to produce the other colors. Combining all three primarylights colors in equal intensities produces white. Varying theluminosity of each light color eventually reveals the full gamut ofthose three lights colors.

Alternative color spaces can be generated using combinations of otherprimary colors. One commonly used color space includes usingcombinations of cyan, magenta, and yellow. While throughout thisapplication, reference will be made to the RGB color space, theprinciples can likewise be applied to other color spaces known in theart.

It should be noted that additive color is a result of the way the eyedetects color, and is not a property of light. There is a vastdifference between yellow light, with a wavelength of approximately 580nm, and a mixture of red and green light. However, both stimulate theeyes in a similar manner, so no difference is perceived by the viewer.

Perception of color is achieved in mammals through color receptors(known as cone cells) containing pigments with different spectralsensitivities (trichromats). In the human eye, the cones are maximallyreceptive to short, medium, and long wavelengths of light and aretherefore usually called S-, M-, and L-cones. L-cones are often referredto as the red receptor, but while the perception of red depends on thisreceptor, micro-spectrophotometry has shown that its peak sensitivity isin the yellow region of the spectrum.

A particular frequency of light stimulates each of these receptor typesto varying degrees. Yellow light, for example, stimulates L-conesstrongly and M-cones to a moderate extent, but only stimulates S-conesweakly. Red light, on the other hand, stimulates almost exclusivelyL-cones, and blue light almost exclusively S-cones. The visual systemcombines the information from each type of receptor to give rise todifferent perceptions of different wavelengths of light.

TABLE 1 Cone type Name Range Peak sensitivity S β (Blue) 400 . . . 500nm 440 nm M γ (Green) 450 . . . 630 nm 544 nm L ρ (Red) 500 . . . 700 nm580 nm

As seen from the Table, the responses from the cones types overlap andare quite broad. Although the peak response of the S-cones is at 440 nm,the eye will barely recognize a chroma difference between light emittedat, for example, 455 nm and light emitted at 465 nm. Moreover, withincertain limits, an almost identical perceived color can be produced by adifferent admixture of slightly different, but separable wavelengths.

FIG. 1 is diagram of a 3-D display system 100 including arear-projection television (RPTV) 102 and a pair of glasses 104 forwearing by a viewer of the RPTV 102. The 3-D display system 100 operatesusing an approach where left eye and right eye digital images areproduced by the RPTV by illuminating, for example, 2-D micro-displaypanels alternatingly with images formed using two separate color spaces,e.g., R₁, G₁, B₁ and R₂, G₂, B₂. In one embodiment, R₁ may be selectedto cover a wavelength range between 600-610 nm; G₁ to cover a wavelengthrange between 520-540 nm; and B₁ to cover a wavelength range between440-460 nm. R₁, G₁, B₁ would be directed, for example, to the right eye.Likewise, R₂ may be selected to cover a wavelength range between 610-640nm; G₂ to cover a wavelength range between 540-550 nm; and B₂ to cover awavelength range between 460-490 nm. R₂, G₂, B₂ would then be directedto the left eye.

The glasses 104 worn by the viewer include a right eye filter 106 and aleft eye filter 108. The right eye filter 106 includes a thin-film notchfilter for each primary color in the color space intended to be viewedby the left eye, for example R₂, G₂, B₂. The left eye filter, similarly,includes a thin-film notch filter for each primary color in the colorspace intended to be viewed by the right eye, for example, R₁, G₁, B₁.Thus, the left eye of the viewer is not able to perceive images formedusing the R₁, G₁, B₁ color space, and the right eye of the viewer is notable to perceive images formed using the R₂, G₂, B₂ color space.

In an alternative embodiment, in addition to, or instead of includingnotch filters, the left eye filter and the right eye filter in theglasses include thin-film band-pass filters targeted to the primarycolors of their respective color spaces. Holographic laser bandpassfilters are fabricated by recording interference patterns formed betweentwo mutually coherent laser beams, unlike conventional interferencefilters, which are made by vacuum evaporation techniques. Thetransmission of holographic filters can reach >90% of S-polarized laserlight with a spectral bandwidth of <2 nm.

FIG. 2 is a block diagram of electronic components of an RPTV 200,according to an illustrative embodiment of the invention. The RPTV 200includes a video input 202, a controller 204, one or more light sources206, and one or more light modulators 208. The video input 202 receivesan image signal encoding a series of left eye image frames and a seriesof right eye image frames for display to a viewer. In variousembodiments, either the video input 202 or the controller 204 decomposeseach right eye image frame and each left eye image frame into at leastone primary color subframe for each primary color used to display therespective image frames. For example, in one implementation, each righteye image frame is split into a sufficient number of primary colorsubframes to provide 8 to 10 bits of grayscale depth per primary color.

The controller 204, in one embodiment is an application specificintegrated circuit. In alternative embodiments, the controller can be ageneral purpose processor, a field programmable gate array, or otherintegrated circuit. The controller 204 controls the light sources 206and the light modulators 208 to display the left eye and right eye imageframes encoded in the image signal.

FIG. 3 is a block diagram of the optical pathway in an illustrative RPTV300, according to one embodiment of the invention. Referring to FIGS. 2and 3, in the RPTV 300, the light source 206 includes a single broadspectrum lamp 302 and a color wheel 304. The color wheel 304 includes aseries of filters corresponding to respective primary colors (e.g., R₁,R₂, G₁, G₂, B₁, and B₂) in the color spaces used to display the left eyeimages and the right eye images. In one embodiment, the color wheel 304includes one filter for each respective primary color. In alternativeembodiments, the color wheel includes multiple filters for eachrespective primary color. In such an embodiment, each filter for a givencolor may be of a different size so that the system may implement apulse width modulation gray scale scheme.

In operation, the color wheel 304 rotates at a rate such that eachfilter comes into the optical path light emitted from the lamp 302 oncefor each right eye image and once for each left eye image received bythe RPTV 300 prior to the display of any images related to a subsequentframe. The overall frame rate is preferably at least 30 Hz, and mayequal to or greater than 60 Hz. Thus, if the RPTV 300 were to operatewith, for example, a 60 Hz frame rate and 4 bits of grayscale depth perprimary color, the controller would have to load 24 distinct primarycolor subframes (4 primary color subframes for each of three primarycolors for a right eye image frame and 4 primary color subframes foreach of three primary colors for a left eye image frame) into the lightmodulator in 1/60th of a second. In one embodiment, the array of lightmodulators includes an array of MEMS mirrors. For example, the array oflight modulators can be a DLP chip developed by Texas Instruments.Alternatively, the array of light modulators can be a liquid crystal onsilicon (LCoS) light modulator array. Display optics 308 project lightreflecting off the light modulator on to a display screen 310 for aviewer to see.

FIG. 4 is a block diagram of an optical path of alternativeimplementation of an RPTV, according to an illustrative embodiment ofthe invention. The RPTV 400 includes six light sources 402. The RPTVincludes one light source 402 for each primary color used to formimages. For example, one light source 402R1 emits a light having awavelength corresponding to a first red color, R1. A second light source402R2 source emits a light having a wavelength corresponding to a secondred color, R2. A third light source 402G1 source emits a light having awavelength corresponding to a first green color, G1. A fourth lightsource 402G2 emits a light having a wavelength corresponding to a secondgreen color, G2. A fifth light source 402B1 source emits a light havinga wavelength corresponding to a first blue color, B1. A sixth lightsource 402B2 emits a light having a wavelength corresponding to a secondblue color, B2.

The display includes one light modulator (either LCoS or DLP) for eachpair of light sources 402. That is, the display includes a lightmodulator 404R for modulating light emitted by both red light sources402R1 and 402R2, a light modulator 404G for modulating light emitted byboth green light sources 402G1 and 402G2, and a third light modulator404B for modulating light emitted by both blue light sources 402B1 and402B2. Display optics 406 redirect the light modulated by the lightmodulators 404R, 404G, and 404B towards a display screen 408. By havingthree times the light modulators than the RPTV 300, the RPTV 400 candisplay three times as many primary color subframes per primary color inthe time allowed for a given image frame, allowing for greater grayscale depth. In operation, the controller alternately loads right eyeimage primary subframes and left image primary subframes into therespective light modulators 404R, 404G, and 404B. In an alternateimplementation, the RPTV 400 includes a separate light modulator foreach light source.

The RPTV 400 has the further advantage over the RPTV 300 in thatseparation between the left and right images can be significantlyimproved by using high brightness, narrow bandwidth light sources in thered, green and blue spectral range. Suitable light sources includelasers, in particular semiconductor diode lasers which directly convertelectric current into photons, and/or optically pumped solid statelasers, and/or non-linear optical elements for frequency-upconversionand/or frequency-mixing. Red, green and blue (RGB) lasers offerdemonstrable benefits over incandescent light sources forhigh-performance imaging applications. Greater color saturation,contrast, sharpness, and color-gamut are among the most compellingattributes distinguishing laser displays from conventional imagingsystems.

Laser sources that are capable of producing the R, G, and B wavelengthscan be, for example, of three types: (1) Gas lasers (e.g., He—Ne for redand Argon for Green and blue); (2) semiconductor diode lasers that emitR, G, and B wavelengths directly; and (3) solid state lasers/oscillatorsthat are optically pumped by semiconductor light sources and emit at oneof the desired wavelengths. Gas lasers are less suitable for theintended application as their emission lines are defined by atomictransitions which are narrow (producing speckle; see below) and may notoffer the desired flexibility in selecting a wavelength for the left andright images. They also have a notoriously low conversion efficiency.

A red/green/blue (RGB) semiconductor/microlaser system, consisting ofthree lasers or laser arrays, each operating at a fundamental color, isan efficient, high brightness, white light projection source.Semiconductor laser operation has been achieved from the UV to the IRrange of the spectrum, using device structures based on InGaAlN, InGaAlPand InGaAlAs material systems. The lasing wavelengths are tunablethrough design of the waveguide and cavity. Desirable center wavelengthranges are 610-640 nm for red, 520-540 nm for green, and 445-470 nm forblue. Laser radiation is inherently narrow band and gives rise to theperception of fully-saturated colors.

The wavelength of semiconductor diode lasers can be adjusted within thegain curve of a semiconductor material by adjusting the composition ofthe material, for example, the Ga:Al:In ratio commensurate with theselection of a suitable, preferably lattice-matched substrate.Lattice-mismatch tends to shorten the operating life of lasers. Thewavelength can in addition be adjusted by suitable choice of waveguideand quantum well thickness, and/or by providing wavelength-selectiveoptical feedback by, for example, adding a DFB or DBR grating.

Unfortunately, narrow band light incident on random rough surfaces (suchas a projection screen) introduces an image artifact known as “speckle.”The visual effects of speckle detract from the aesthetic quality of animage and also result in a reduction of image resolution. Consequently,in the context of high resolution display systems, it is desirable thatspeckle be reduced or eliminated.

Preferably, the spectral bandwidth for a projection display lightsource, such as light sources 402R, 404G, and 404B, are on the order ofseveral nanometers (i.e., 1-5 nm). Such a light source could beconsidered quasi-monochromatic, i.e., sufficiently broadband for thereduction of speckle yet sufficiently narrow band for color purity andto be discriminated by the glasses worn by the viewer.

FIG. 5 is a block diagram of one suitable light source for use in theRPTV 400. As described in U.S. Pat. No. 6,975,294 (the entirety of whichis incorporated herein by reference), and as depicted in FIG. 5, abandwidth-enhanced laser imaging system 500 includes a plurality oflasing elements 502, with each lasing element 502 emitting a laser beamwith a center wavelength λ_(0i) and a spectral bandwidth Δλ_(i). Thelasing elements 502 are allowed, by design, to have a slightly differentcenter wavelength λ_(0i), thereby creating an ensemble bandwidth ΔΛwhich is greater than the bandwidth Δλ_(i) of any individual lasingelement 502 in the array.

Imaging optics 504 combine the respective laser beams 506. The lasingelements 502 can include semiconductor lasers that are arranged in acommon emission plane, for example, forming a two-dimensional array. Thelasing elements 502 can emit R, G, B visible light or UV or IR opticalradiation.

For the third type of laser, solid state lasers/oscillators areoptically pumped by semiconductor light sources, the system may alsoinclude an optical frequency converter, such as bulk crystals orwaveguides that are phase matched or quasi-phase matched (QPM) andpumped by the (optionally bandwidth-enhanced) semiconductor lasingelements. Alternative light sources may also include arrays ofdiode-pumped solid state and fiber lasers. The ensemble spectrum A canhave an ensemble bandwidth ΔΛ between 0.5 nm and 10 nm.

Visible light emission using PP (Periodically Poled) nonlinear materialsmay also be suitable as light source technology for the RPTV 400.Crystals that cannot be phase-matched because of the lack of adequatebirefringence to offset dispersion can be phase-matched by modulatingthe sign of the nonlinear coefficient. Periodically poled LiNbO₃, forexample, can be quasi-phase-matched over the entire transparency rangefrom less than 400 nm to greater than 4000 nm. Other suitable nonlinearcrystals are, inter alia, PP KTP and PP RTA. Furthermore, the crystalorientation can be selected to optimize the nonlinear interaction. PPchips may be operated so as to generate second harmonic radiation (SHG)or sum frequency radiation (SFG).

The wavelength of GaAlInAsP lasers can be varied between orange and IRby selecting the respective Ga:Al:In and As:P ratios. Alternately, usingsemiconductor diode lasers in combination with PP nonlinear crystals orwaveguides, red light can be efficiently produced from a suitable diodelaser, such as AlGaAsP. Blue could be produced by frequency-doubling 910nm or 930 nm laser light output from a GaInAlAs strained-layer quantumwell (QW) laser, giving a wavelength of 455 nm and 465 nm, respectively.Green laser emission could be produced in two ways: (1) byfrequency-doubling 1060 and 1080 nm to attain doubled wavelengths of 530and 540 nm, respectively; and (2) by sum-frequency mixing of light fromlasers emitting between 820 and 840 nm with light from lasers emittingbetween 1420 and 1450 nm. In the latter case, the desired wavelength canthen be attained by suitable selection of one respective laser from eachof the two wavelength ranges. For example, the combination of 820 nmwith 1420 nm produces ˜520 nm in a PP—LiNiO₃ crystal or waveguide,whereas the combination of 840 nm with 1450 nm produces ˜540 nm. Lightfrom multiple lasers with slightly offset wavelengths can be combined,as described above and in U.S. Pat. No. 6,975,294, to produce laseremission with ensemble spectra broad enough to suppress speckle, butnarrow enough to produce the well separated emission peaks in the R, G,B spectral range for use in RPTV applications.

In another implementation, the light sources 404R, 404G, and 404B arenarrow bandwidth, red, green and blue LED's instead of lasers. Becausethese LED's have a greater light emission bandwidth than lasers, theymay not produce speckle.

FIG. 6 is a graph illustrating wavelengths of light sources for use inan illustrative embodiment of the invention. As described above, theRPTV 200, 300, or 400 preferably forms images using two substantiallysimilar, but distinguishable, wavelengths of three or more primarycolors. In one illustrative embodiment or RPTV 400, the lights sources402 emit light having a bandwidth centered at the following wavelengths:

TABLE 2 Primary Color Center Wavelength R1 635 nm R2 645 nm G1 520 nm G2530 nm B1 455 nm B2 465 nm

In summary, methods and systems are described which are able to producepolarization-independent full color images suitable for rear-projectiontelevision sets and other multimedia displays. The system usesillumination with R, G, B light from two different light sources foreach color. The viewer wears glasses with narrowband optical filters,preferably holographic filters. The R, G, B light from the light sourcesis slightly offset at each of the 3 emission wavelengths, with one setof R, G, B light being filtered by the holographic filter in front ofthe left eye of the, and the other set of R, G, B light being filteredby the holographic filter in front of the viewer's right eye.

The invention may be embodied in other specific forms without departingform the spirit or essential characteristics thereof. For example, theinvention described above can also be implemented with rear projectiontelevisions employing other forms of modulators as well as with variousdirect view and projection displays. The forgoing embodiments aretherefore to be considered in all respects illustrative, rather thanlimiting of the invention.

1. A method of displaying a three-dimensional image comprising:displaying a first series of right eye images by illuminating a lightmodulator with a first color; displaying a first series of left eyeimages, wherein each image in the first series of left eye imagescorresponds to a respective image in the first series of right eyeimages, by illuminating the light modulator with a second color, whereinthe first color is substantially the same as, but not identical to, thesecond color; and providing a viewer with a left eye filter forfiltering out the first color and right eye filter for filtering out thesecond color.
 2. The method of claim 1, comprising displaying a secondseries of right eye images, wherein each image in the second series ofright eye images corresponds to a respective image in the first seriesof right eye images, by illuminating a second light modulator with athird color, wherein the third color is substantially different from thefirst and second colors.
 3. The method of claim 2, comprising displayinga second series of left eye images, wherein each image in the secondseries of left eye images corresponds to a respective image in the firstseries of left eye images, by illuminating the second light modulatorwith a fourth color, wherein the fourth color is substantially differentfrom the first and second colors and is substantially the same as, butnot identical to, the third color.
 4. The method of claim 3, wherein thefirst and second light modulators are the same light modulator.
 5. Themethod of claim 3, wherein the first and second light modulators aredifferent light modulators.
 6. The method of claim 3, wherein the lefteye filter filters out the third color and the right eye filter filtersout the fourth color.
 7. The method of claim 3, wherein the first andsecond colors are both perceived by the viewer as one of red, green,blue, magenta, cyan, and yellow.
 8. The method of claim 7, wherein thethird and fourth colors are both perceived by the viewer as a differentone of red, green, blue, magenta, cyan, and yellow.
 9. The method ofclaim 1, wherein illuminating comprises activating a laser.
 10. Themethod of claim 1, wherein illuminating comprises activating a lightemitting diode.
 11. The method of claim 1, wherein illuminatingcomprises directing light through a portion of a color wheel.
 12. Themethod of claim 1, wherein the first color includes light having a firstcenter wavelength and the second color includes light having a secondcenter wavelength, wherein the first center wavelength differs from thesecond center wavelength by about 10 nm.
 13. The method of claim 1,wherein the first color includes light in a bandwidth that does notoverlap with the bandwidth of the light included in the second color.14. A system for displaying a three-dimensional image comprising: afirst light source providing a first illumination color; a second lightsource providing a second illumination color substantially the same as,but not identical to, the first illumination color; a light modulatorfor modulating light emitted by the first and second light sources togenerate first and second series of images, wherein each image in thefirst series of images corresponds to a respective image in the secondseries of images; and projection optics for displaying the first andsecond series of images on a display screen.
 15. The system of claim 14,wherein the first light source comprises a laser.
 16. The system ofclaim 14, wherein the first light source comprises a light emittingdiode.
 17. The system of claim 14, wherein the first light sourcecomprises a lamp and a first portion of a color wheel and the secondlight source comprises the lamp and a second portion of a color wheel.18. The system of claim 14, wherein the first light source comprises aplurality of lasers and optics for combining the light output by theplurality of lasers to form the first illumination color.
 19. The systemof claim 18, wherein the second light source comprises a secondplurality of lasers and optics for combining the light output by thesecond plurality of lasers to form the second illumination color. 20.The system of claim 19, wherein the bandwidth of light in the firstillumination color is centered at a wavelength that is about 10 nm apartfrom a center wavelength of the light included in second illuminationcolor.
 21. The system of claim 14, wherein the light modulator comprisesan array of micromirrors.
 22. The system of claim 14, wherein the lightmodulator comprises a liquid crystal on silicon light modulator.
 23. Thesystem of claim 14, comprising a processor for alternately addressingthe light modulator with images from the first series of images and thesecond series of images.
 24. The system of claim 14, comprising thirdand fourth light sources and a second light modulator for modulatinglight emitted by the third and fourth light sources, wherein the thirdlight sources emits a third illumination color which is substantiallythe same as, but not identical to, a fourth illumination color emittedby the fourth light source, and the third and fourth illumination colorsare substantially different from the first and second illuminationcolors.
 25. The system of claim 14, comprising viewing glasses includinga left eye filter for filtering out the first series of images and aright eye filter for filtering out the second series of images.
 26. Thesystem of claim 25, wherein the left eye filter comprises a thin filmnotch filter.
 27. The system of claim 25, wherein the left eye filtercomprises a plurality of thin film notch filters.
 28. The system ofclaim 27, wherein the right eye filter comprises a plurality of thinfilm notch filters.
 29. Apparatus for viewing three-dimensional imagescomprising: a first plurality of filters for filtering out a first setof colors emitted by a display and for allowing a second set of colorsemitted by the display to pass through the first plurality of filters; asecond plurality of filters for filtering out a second set of colorsemitted by the display and for allowing the first set of colors emittedby the display to pass through the second plurality of filters; whereineach color in the first set of colors is substantially the same as, butnot identical to a respective color in the second set of colors; and aframe for positioning the first plurality of filters in front of theleft eye of a viewer and the second plurality of filters in front of theright eye of a viewer.
 30. The apparatus of claim 29, wherein pairs ofrespective colors in the first and second sets of colors correspond torespective primary colors used to form an image.